Reluctance machines are well known in the art. These machines operate on the tendency of the machine's rotor to move to a position where the reluctance with respect to the stator is minimized (in other words, where the inductance is maximized). This position of minimized reluctance occurs where the rotor pole is aligned with an energized stator pole. When operated as a motor, energizing the stator pole generates a magnetic field attracting the closest rotor pole towards the stator pole. This magnetic attraction produces a torque causing the rotor to rotate and move towards the minimized reluctance position. Conversely, when operated as a generator, torque applied to the rotor is converted to electricity as the rotor pole moves away from the aligned position with respect to an energized stator pole.
The generation of magnetic flux requires electric current. The magnetization of a relatively larger are requires a relatively larger magnetization current. As the rotor moves, the magnetic flux varies. The existence of such a time varying magnetic flux initiates losses known in the art as “core loss” (eddy current loss and hysteretic loss). In order to minimize overall loss in a switched reluctance machine, it is desired to minimize the magnetized area of the rotor and stator cores. In a conventional switched reluctance machine, however, the design of the rotor and stator along with the design of the stator windings do not provide for an optimal magnetization pattern with respect to the core, and thus such a machine cannot achieve higher levels of efficiency. In this regard, the magnetic flux pattern in such prior art machines exhibits a characteristic long flux path which passes radially across the rotor between two simultaneously actuated stator poles and circumferentially around the stator back iron. While shorter flux paths may also be present from time to time as the rotor moves, it is the long flux path between the simultaneously actuated stator poles across the radius of the rotor which dominates the machine's efficiency calculation.
There is accordingly a need in the art for a switched reluctance machine that is configured to emphasize shorter magnetic flux paths.